fix(settings): Show available update in Updates panel

[charlesvien]

Problem

Clicking "Check now" in Settings > Updates while an update is available leaves the row stuck on "Checking for updates...", even though the rest of the app shows the update banner.

Changes

When a check finds an update, the updates service emits a status with checking: false, available: true, but deriveUpdateStatus had no case for it, so the stale checking message was never replaced. Added an available case ("Update x.y.z available") and an error case so async check failures (e.g. timeouts) no longer leave the row stuck either.

How did you test this?

Unit tests for the new cases (vitest run src/settings/updateStatus.test.ts, 14 passed), plus full pnpm typecheck and Biome lint.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

[trunk-io]

😎 This pull request was merged.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 233f3bc.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "show available update status in settings..." | Re-trigger Greptile}

[github-actions]

Small, contained fix adding two missing status cases (available/error) to a pure derive function, with matching unit tests; no risky territory touched and no unresolved concerns.

• 👍 on the PR from greptile-apps[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	15L, 1F substantive, 50L/2F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1b-small (50L, 2F, single-area, fix)
stamphog 2.0.0b3		.stamphog/policy.yml @ ed26e21 · reviewed head 233f3bc

[github-actions]

Could not verify team-posthog-code membership (GitHub API error). Auto-release is limited to members of the team-posthog-code GitHub team, so this will ship with the next scheduled release instead.